Article excerpt

INTRODUCTION

Recently, a great deal of attention has been given to the incorporation of a highway-in-the-sky (HITS) display as the primary cockpit flight display. A HITS (also called "pathway") display provides course guidance to the pilot using a perspective view of a path through the air. HITS displays are expected to replace traditional "round dial" cockpit instrumentation in the near future. Figures 1a and 1b provide examples of typical HITS displays.

The effectiveness of HITS displays for improving both horizontal and vertical guidance, as compared with current navigation displays, is well established (Haskell & Wickens, 1993; Jensen, 1981; Wickens & Prevett, 1995). Also established is the utility of HITS displays for flying nonstandard instrument approach procedures (Barrows, Enge, Parkinson, & Powell, 1996; Grunwald, 1996; Reising, Liggett, Solz, & Hartsock, 1995). Implementation of these procedures will allow, for example, curved approaches into airports that do not have published instrument approach procedures because of dangers presented by terrain or other obstacles.

To assist in the widespread implementation of these displays in the cockpit, researchers have studied factors that influence their overall effectiveness. Studies have been conducted to determine optimal pathway symbology and field-of-view values (e.g., Barfield & Rosenberg, 1992) and to determine which cues are employed by pilots to maintain their position on the pathway (e.g., Theunissen & Mulder, 1995).

One issue that is critical to successful implementation of HITS displays is the effect that these displays have on pilot situation awareness (SA). Problems with SA have been implicated as a leading causal factor in both military aviation mishaps (Endsley, 1997) and accidents among major air carriers (Endsley, 1995). Some research has already been done on the effect of HITS displays on pilot SA (Dorighi, Ellis, & Grunwald, 1993; Kramer & Busquets, 2000). This research has primarily focused on the awareness of the relative location of stationary objects outside the cockpit (e.g., runways, land-marks). Findings from these studies have shown mixed results, sometimes demonstrating an improvement in SA and sometimes a decrement.

The current study focuses on three types of pilot SA and how these are effected by the use of a HITS display. The first type of SA is awareness of the position of the intended flight path relative to the current position of the aircraft. Endsley (1997) referred to this type of SA as spatial/temporal SA. The HITS display depicts a volume of space representing the intended flight path of the aircraft. Positioning the aircraft on the pathway is therefore equivalent to positioning the aircraft on the intended flight path. Wickens (1995) suggested that one of the major deficiencies of three-dimensional (3D) perspective displays, of which the HITS display is one example, is the "ambiguity of position estimate along the line of sight or viewing vector of the display" (p. K2-9). When approaching the pathway from the outside, the pilot has very few visual cues that indicate distance cues, such as binocular disparity and textural gradients, are unavailable. Other cues, such as relative size, can be distorted. These fac tors could make it difficult for a pilot to intercept a pathway when approaching from outside the pathway. The ability of the pilot to maintain awareness of the position of the aircraft relative to the pathway is important. The present study was designed to provide information on the effects that different pathway formats and guidance cues have on the ability of pilots to establish their aircraft on the pathway.

A second type of SA addressed here is the awareness of other aircraft in the area. Referred to as tactical SA (Endsley, 1997), the need to maintain awareness outside the cockpit is critical to flight safety. …